DE102012220257A1 - Transparent ceramics - Google Patents

Abstract

The present invention is a transparent ceramic, process for their preparation and their use.

Description

The present invention is a transparent ceramic, process for their preparation and their use.

The invention relates to a transparent ceramic high strength, which all transparent ceramic materials, such. Mg-Al spinel, AION, yttrium aluminum garnets, yttria, zirconia, etc. Particularly interesting are the materials with increased mechanical strength and in particular protective ceramics, such as Mg-Al spinel, AION, alumina, etc.

To z. B. vehicles, such as military vehicles or in part to protect civil vehicles from fire, they are armored. The armor is usually done by means of a metal or a metal-ceramic system. However, such systems are not possible for the areas containing windows, such as side windows, windscreens or the like. These areas are, for example, equipped with bulletproof glass. However, armored glass is known to have a significantly lower ballistic efficiency compared to hard core ammunition than composite or metal armor systems. As a result, the window panes equipped with bulletproof glass are weak points of the vehicle. A sufficient protection performance can only be achieved by using very large weights, which significantly reduces the mobility of vehicles as well as admission limits.

Transparent ceramic has an improved protective behavior compared to bulletproof glass. For this reason, looking for alternatives to bulletproof glass relatively early. These were mainly found in ceramics such as spinel and AION. These ceramics have improved mechanical properties, such as increased strength and hardness, compared to bulletproof glass. In the known ceramics, however, it is difficult, in contrast to bulletproof glass, to produce virtually defect-free components. Most of the components made of transparent ceramics contain individual larger defects> 100 μm.

Examples of such defects are in particular pores, due to pores in the starting powder for the transparent ceramics, and Granulatrelikte, pressing errors, degassing, organic inclusions, o. The like. Although these defects do not necessarily affect the transparency measurement, but they are obstructive for the view and thus to avoid. Inclusions, which are not reliably avoidable, especially in pressing processes, reduce the usefulness of the ceramic material, especially when used as a transparent ceramic protective material. There is also another effect:
In "International Journal of Impact Engineering", 27.5.2002, 509-520 z. B. reports that the HEL (Hugenostic Elastic Limit) is a crucial factor in the effectiveness of ceramics as ballistic protection. In addition, a strong influence of porosity on the HEL is found. Larger pores - in number and specific size - reduce the HEL and thus the protective effect.

In "Ceramic Engineering and Science Proceedings", 26:77, 2005, 123-130 is described that the porosity is harmful, as it is identified as the trigger of a material flow and thus the destruction of the ceramic.

In addition, it has been shown that strength is an essential parameter for the installation of transparent ceramics panes in vehicles, since mechanical strength, such as stone chipping or twisting of the vehicle, requires adequate strength. Since the desire generally for relatively thin ceramic layers, a correspondingly high strength is desirable in order to realize thin slices can. That is, the strength of the entire component - usually in the form of individual tiles - is extremely relevant for use. Since the greatest error is relevant to the failure of ceramic components, high strength on small individual samples does not provide adequate information.

A high four-point bending strength is a good measure to characterize the component. In order to meet the higher strength requirements according to the invention, there must be no large structural error in the four-point bending samples, so that the probability of corresponding errors in larger components is reduced. In order to fulfill the minimum requirement, four-point bending tests are carried out after DIN EN 843-1 no error> 100 μm, better no error> 20 μm.

In previous developments, attempts were always made to realize components with increased strength. MER Corporation, Tucson, Ariz., USA, has prepared a spinel having a four point bending strength of about 300 MPa. In hot-pressed components, which are usually produced with the aid of LiF, the pores have a smooth surface which promotes transparency and are therefore not visually disadvantageous. By means of microscopic analysis, however, it can be shown that larger pores are present, and in addition the large crystals due to the high process temperatures also have a strength-lowering effect. The maximum four-point bending strengths average ≤ 300 MPa (MER specifications). Also according to the EP 1 557 402 A2 produced ceramics with particle sizes <1 micron seem to have the strength reducing elements, since there stated strengths of 200-250 MPa are even below the strengths of hot-pressed components. Although no sizes of individual inclusions are disclosed, but the low strength causes such inclusions, since even with particle sizes of ≥ 50 microns higher strengths can be measured.

By means of SPS (= spark plasma Sintering), like it in "Condition Optimization for Producing Transparent MgAl2O4 Spinel Polycrystal"; J. Am. Ceram. Soc; 92 (6) 1208-1216 (2009), Morita et al., although strengths of around 400 MPa can be achieved; However, the components described here at a light wavelength of 600 nm RIT <70%, so they are not suitable for use as a transparent protection o. The like. This means that high strengths can not yet be combined with the necessary high RIT> 75%.

The present invention improves the applications of transparent ceramic under increased mechanical stress and thus enables the more efficient use of this ceramic, since z. As thinner components can be manufactured and used, but can meet the same function as thicker components with lower strength by their lower tendency to fracture. This advantage becomes particularly clear when used as ballistic protection.

Another important parameter for the quality of a transparent ceramic is the scattering loss in the ceramic. Scattering losses in the ceramic are caused by stains in the ceramic. In order to minimize scattering losses in the ceramic as low as possible, the smallest possible stain frequency is therefore essential. Only thereby is it possible to achieve a corresponding optical quality for numerous applications such as optical lenses, protective glasses, sight glasses, lasers in the wear area, etc. If the number of scattering centers is too large or too large in general, the optical quality of a transparent ceramic is drastically reduced.

For example, this leads to irritation of the driver / plant operator in the case of transparent protective windows or wear-resistant windows. That means that the ergonomics are negatively influenced here. With lenses, lasers or other optical precision systems, performance and precision are negatively affected. Thus, it is imperative to ensure a certain optical quality.

Causes of such spots / scattering centers may be secondary phases caused by chemical contaminants or processing errors.

The invention is therefore based on the object to provide transparent ceramics with high strengths, which is paired with a high transparency (RIT> 75%) and high optical quality.

This object is achieved by the features of claim 1. Preferred embodiments or further developments of the invention are characterized in the subclaims.

Surprisingly, the object underlying the invention could be achieved by a ceramic whose mean grain size moves in a certain range. It was found that the performance of a ceramic can be surprisingly improved in the sense of the present invention, if instead of a ceramic with very fine average grain sizes, for example, if instead of a ceramic with average grain sizes in the range of <1 .mu.m, a ceramic with average grain sizes in Range of> 10 to ≤ 100 microns, preferably a ceramic with average grain sizes in the range of> 10 to 50 microns, more preferably a ceramic with average grain sizes in the range of> 10 to 20 microns, most preferably a ceramic with average grain sizes in the range from 11 to 20 microns, which has a high transparency (RIT> 75%) and a high optical quality.

The raw materials to be used according to the invention have an average primary particle size d50 of <2 μm, preferably of 5 to 500 nm and a purity of> 99.5%, preferably of> 99.9%, ie. H. largest contamination <0.5% and <0.1%, respectively.

According to the invention, particular preference is given to using raw materials with a low tendency to agglomerate.

The mean grain size is determined by the line-cut method according to DIN EN 623 which determines RIT value on a 2 mm thick, polished disk with light of the wavelength of 600 nm.

The high optical quality is characterized in the context of the present invention by the degree of spotting frequency, determined by the method described below. A preferred ceramic according to the invention has a stain frequency of <10%, a particularly preferred ceramic according to the invention has a stain frequency of <1%.

Another essential aspect of transparent ceramics is the need for good polishability and further processing of the ceramics, since this significantly influences a large proportion of the overall costs. It was surprisingly found that in a ceramic according to the invention with average particle sizes in the range of> 10 to ≤ 100 microns, especially in a ceramic according to the invention with average particle sizes in the range of> 10 to 20 microns not starting with ceramics with average particle sizes in the range of <10 microns relevant fine grain hardening can be determined. The known in the prior art ceramics with average grain sizes in the range of <10 microns significantly onset fine grain hardening not only complicates the processing of the ceramic but also deteriorates the fracture behavior.

This is surprising in that the hardness of the ceramics according to the invention is lower than the ceramics with finer average particle sizes known in the prior art.

Another advantage of the ceramic according to the invention is its particularly good ballistic performance, which was found by bombardment tests in comparison to fine-crystalline ceramic (particle size <1 micron). The ballistic advantages of the ceramic according to the invention are particularly surprising since their hardness is lower, but the fracture behavior is better than that of the very fine ceramics known from the prior art (eg. EP 1 557 402 A2 . DE 10 2004 004 259 ). On the other hand, however, both the hardness and the fracture behavior of the ceramic according to the invention in comparison to the known coarsely crystalline ceramic (eg. US 2004/0266605 . US 5,001,093 . US 4,983,555 ) better. Furthermore, especially the multiple bombardment is favored (multihit resistance), ie the triangular bombardment of a transparent ballistic target produced from the ceramic according to the invention.

An average grain size in the inventive range of> 10 to ≦ 100 μm, in particular a mean grain size in the inventive range of> 10 to 50 microns also allows optimal processing, easier cutting (eg water jet) than with finely crystalline material (lower hardness than fine crystalline material), simplified grinding, polishing against coarse-grained material (the erupting crystals are smaller). The simplified processing allows important freedom in the later design of any free-form surfaces. This is of particular interest in the design of curved windows for civil protected vehicles.

Another advantage of the ceramic according to the invention lies in the significantly lower production costs, since coarser and thus cheaper powder can be used (the average (final) grain size is in the range of> 10 to ≤ 100 microns), an optimal hard machining and cheaper manufacturing processes possible are. Since the raw materials make up the largest share of the manufacturing costs in a general economic production process, it is precisely through the use of coarser raw materials that it is possible to produce a significantly cheaper product.

Especially the price of the known from the prior art transparent ceramics has previously denied a more extensive market entry in ballistics. So far, either the hot pressing used, the fine nanopowder, which are necessary for production via other routes or the extremely expensive polish causes extremely high prices.

• • transparente Keramik mit einer an einer 2 mm dicken, polierten Scheibe mit Licht der Wellenlänge von 600 nm gemessenen RIT > 75% mit mittleren Korngrößen im Bereich von > 10 bis ≤ 100 μm, vorzugsweise eine transparente Keramik mit mittleren Korngrößen im Bereich von > 10 bis 50 μm, besonders bevorzugt eine transparente Keramik mit mittleren Korngrößen im Bereich von > 10 bis 20 μm, ganz besonders bevorzugt eine transparente Keramik mit mittleren Korngrößen im Bereich von 11 bis 20 μm; Bevorzugt ist eine wie oben beschriebene transparente Keramik, die
• • eine hohe optische Qualität aufweist;
• • eine Fleckenhäufigkeit von < 10%, besonders bevorzugt eine Fleckenhäufigkeit von < 1% aufweist;
• • eine Zweitphase, deren Größe maximal < 2000 μm, vorzugsweise < 200 μm ist, aufweist;
• • eines der Oxide aus Zirkon, Aluminium, Magnesium, Yttrium, Zink, Zinn, Calcium, Titan, Gallium, Indium, Hafnium, Scandium, Cer, Europium, Barium oder Kombinationen daraus enthält;
• • Mg-Al-Spinell, AION, Aluminiumoxid, Yttriumaluminium Granate, Yttriumoxid, Zirkonoxid enthält;
• • ALON enthält;
• • eine Spinellkeramik ist.

The subject of the present invention is therefore in detail:

• Transparent ceramics with a RIT> 75% with mean grain sizes in the range of> 10 to ≤ 100 μm measured on a 2 mm thick, polished disk with light of the wavelength of 600 nm, preferably a transparent ceramic with mean grain sizes in the range of> 10 to 50 microns, more preferably a transparent ceramic with average particle sizes in the range of> 10 to 20 microns, most preferably a transparent ceramic with average particle sizes in the range of 11 to 20 microns; Preferred is a transparent ceramic as described above
• • has a high optical quality;
• • has a stain frequency of <10%, more preferably a stain frequency of <1%;
• A second phase whose size is at most <2000 μm, preferably <200 μm;
• • one of the oxides of zirconium, aluminum, magnesium, yttrium, zinc, tin, calcium, titanium, gallium, indium, hafnium, scandium, cerium, europium, barium or combinations thereof;
• • Mg-Al spinel, AION, alumina, yttrium aluminum garnet, yttria, zirconia;
• • ALON contains;
• • is a spinel ceramic.

The ceramic according to the invention can be used for example in ballistics.

The invention will now be clarified by way of example.

Example 1:

It is processed spinel powder (MgAl ₂ O ₄ ) to a 50-Ma% slip. The thin-viscous slurry is then sprayed by means of an eccentric screw pump in a fluidized-bed granulation plant. As powder bed, the pure powder is first added to the system. By a slow and continuous slip supply is The material is slowly continuously granulated The pressure conditions and the supply air are adjusted so that granules in the size range between d10 = 100 μm and d90 = 300 μm are produced. The granules produced in this way are granules which have no inhomogeneities, such as hollow spherical structure or donut form. The granules are then uniaxially pressed at 160 MPa into a 50 mm x 50 mm plate which, due to its homogeneity, can be densely sintered at 1500 ° C. Thereafter, a HIP process is also carried out at 1500 ° C and 2000 bar. After the HIP process, a measured density of 3.575 g / cm ³ results. the analogous to DIN EN 623-2 determined by the Archimedes method. This represents a density of> 99.9%. The high homogeneous density results in a RIT value of 83% - with 0.2% fluctuation within the produced board. The existing stain content is ≤ 0.5%. The according to the line-cutting method after DIN EN 623 determined average grain size of the ceramic is after a thermal etching of the polished samples 12 microns +/- 0.5 microns.

The ceramics according to the invention thus produced are examined in more detail by the method described below for stain analysis and isolated according to the desired specification.

Method for stain analysis:

In the production of the transparent ceramics, it is found that most of the samples do not produce clear test specimens, but that all samples are interspersed with patches in the size range between a few μm and several 100 μm. For this reason, there is a need to analyze and quantify them since they are a hindrance to the visual appearance of the later component made of the ceramic of the present invention. It also shows that different samples are interspersed to different degrees with these spots. One such example is in shown.

On closer inspection, some patches appear more like cracks or globular shapes or larger gussets. Causes of such errors can be chemical contamination, pressing errors or other processing errors. The macroscopic patches thus appear due to the scattering in these areas. There seems to be a direct connection between relics in the green, impurities and the later spots.

The stain analysis procedure described below provides information on stain size distribution, stain frequency and the sum of stains within the sample. For this purpose, the sample center or the sample surface is focused in the light microscope and an image is taken. This image is subdivided into white and black areas via automated image processing, so that a clear visual difference between spots and transparent areas can be recognized. Typical images after microscopic analysis (left) and after image processing (right) are in to see. Use is a 6.3x magnification and a screen area of 1280 x 1024 pixels.

This image is then processed by means of image processing software and an Excel routine with regard to patch frequency distribution and surface area (inclusions as a proportion of the total area E _F ) ( ) evaluated. The mean inclusion size is E _D50 .

The accuracy of the evaluation is determined by the resolution (default 1280 x 1024 pixels) and the error size and magnification.

Bei der am häufigsten verwendeten 63-fachen Vergrößerung ergibt sich eine Genauigkeit von +–0,9 μm für E_D50. Für den Flächenanteil E_F +–2,72 μm² oder +–7,6·10^–5%. Da die Vorgehensweise festgelegt ist, ist eine hohe Reproduzierbarkeit der Ergebnisse auch dann gewährleistet, wenn teilweise Flecken durch die Bildbearbeitung verschwinden.It is for

At the most commonly used 63x magnification, the accuracy is + -0.9 μm for E _D50 . For the area fraction E _F + -2.72 μm ² or + -7.6 × 10 ^-5 %. Since the procedure is defined, a high reproducibility of the results is guaranteed even if some spots disappear through the image processing.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1557402 A2 [0009, 0024]
• DE 102004004259 [0024]
• US 2004/0266605 [0024]
• US 5001093 [0024]
• US 4983555 [0024]

Cited non-patent literature

• DIN EN 843-1 [0008]
• "Condition Optimization for Producing Transparent MgAl2O4 Spinel Polycrystal"; J. Am. Ceram. Soc; 92 (6) 1208-1216 (2009), Morita [0010]
• DIN EN 623 [0020]
• DIN EN 623-2 [0031]
• DIN EN 623 [0031]

Claims (11)

Transparent ceramic, characterized in that it has a measured on a 2 mm thick, polished disc with light of wavelength 600 nm RIT> 75% and average grain sizes in the range of> 10 to ≤ 100 microns. Transparent ceramic, characterized in that it has a measured on a 2 mm thick, polished disc with light of wavelength 600 nm RIT> 75%, average particle sizes in the range of> 10 to ≤ 100 microns and a high optical quality. Transparent ceramic according to claim 1 or 2, characterized in that it has average particle sizes in the range of> 10 to 50 microns. Transparent ceramic according to claim 1 or 2, characterized in that it has average particle sizes in the range of> 10 to 20 microns. Transparent ceramic according to one or more of claims 1 to 4, characterized in that it has a stain frequency of <10%, more preferably a stain frequency of <1%. Transparent ceramic according to one or more of claims 2 to 5, characterized in that it has a second phase whose size is at most <2000 microns, preferably <200 microns has. Transparent ceramic according to one or more of claims 1 to 6, characterized in that it is one of the oxides of zirconium, aluminum, magnesium, yttrium, zinc, tin, calcium, titanium, gallium, indium, hafnium, scandium, cerium, europium, barium or combinations thereof. Transparent ceramic according to one or more of claims 1 to 6, characterized in that it contains Mg-Al spinel, AION, alumina, yttrium aluminum garnets, yttria or zirconia. Transparent ceramic according to one or more of claims 1 to 6, characterized in that it contains ALON. Transparent ceramic according to one or more of claims 1 to 6, characterized in that it is a spinel ceramic. Use of a transparent ceramic according to one of claims 1 to 10 in ballistics.

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